The presently existing basic design of high-powered combustion engines consists of two main cast components: the cylinder block and the cylinder head. Bored out cylinders in the block and portions of the head form combustion chambers. The function of the combustion chamber is to contain the firing pressure, to pressurize the piston crown, guide the piston and transfer the absorbed combustion heat to a coolant.
One existing design involves the use of a separate cylinder liner and coolant jacket with numerous mechanical joints, seals and other attachment components to secure the cylinder head to the liner. In one current commercial diesel engine of this design, a total of 42 components are used to join, seal and position the liner, jacket, cylinder head and block. These components are primarily required to seal and withstand the high combustion pressures and temperatures, as well as provide aligned and leak tight passages for coolant flows acting between the block and head. These attachment, sealing and alignment components are generally the highest stress and highest temperature points in the engine. A careful design, trading increased material in some areas (to lower the stress) with decreased material in other areas (to lower temperature by reducing resistance to heat transfer) must be accomplished.
For engines required for long term operation or heavy-duty service, various components have been made replaceable. Materials have also been substituted for the traditional cast iron. Of specific interest among these components are steel liners. Centrifugal casting and careful material selection is able to significantly improve wear resistance at a moderate cost increase, but additional seals, collars and machining of the block for sealing surfaces is again required.
Liners have also been used as a retrofit in previously unlined cylinders to add life. The worn cylinder block is bored to a larger diameter and a steel liner inserted. This could only be accomplished in cylinder block with thick walls capable of being bored out. Again, additional seals, collars and machining operations are required.
Although steel liners have significant strength and wear life advantages in new and retrofit applications, they can create additional cooling problems. Cooling is one of the primary functions of the cylinder wall since few engineering materials can withstand combustion flame temperatures. This liner, when backed by the cylinder without direct cooling, now presents an additional resistance to heat flow. Especially at the interface between the liner and block. The additional collars, retainers and seals causes hot spots and resistance to heat flow. The seals may also require lower temperatures to function properly, further compounding the cooling problems. In a retrofit application, these added cooling and other components require space, which can reduce displacement and performance.
In addition to the direct cooling problems caused by traditional liners and related hardware, differential thermal expansion can cause additional stress. The additional resistance to heat flow at seals, retainers and joints results in temperature differences at different points in the liner and block. Because of thermal expansion in the liner and associated hardware, the support by the block creates additional stresses.
Although one-piece combustion chamber construction is not new, it has been avoided in the past. Reasons for avoiding one piece construction include manufacturing cost (machining access to valve seats, guides, cylinder bore), material incompatibility (cast iron is not generally weldable) and cooling. Differential thermal expansion can create large stress in one-piece combustion chambers unless uniformly cooled. Casting tolerances, weld beads, and ports create discontinuities leading to hot spots.
One of the most important reasons for not using one-piece construction is the constraints on repair/replacement. Access to high wear/deposit areas, such as valves, pistons, valve seats and cylinders, is necessary for long term performance. One-piece construction limits access to these critical areas.
Simply welding liners to the head would eliminate many pieces of attaching equipment but would result in difficult, if not impossible cooling problems. Liner thickness would have to be significant in order to withstand high thermal and differential stresses.
Welded liners would have additional problems in a retrofit application. Tolerances on the liner and bored out cylinder would require perfect alignment, roundness and positioning. Because of increased resistance to heat flow, differential thermal stresses would be increased. If the internal combustion engine is a two cycle design with air intake ports in the cylinder wall, retrofit with a liner now also requires air seals and rotational alignment of the liner.
In summary, prior art one-piece combustion chamber engines cannot be easily repaired/replaced, while cylinders bored within blocks or liners attached to blocks require many gaskets, seals, attachment and alignment components. These components reduce reliability and add cost and time to assembly/disassembly procedures. The components also produce stress concentration points and hot spots requiring increased weight and cooling system performance.